Method and Apparatus For Multi-Axis Waterjet/Abrasivejet Cutting

ABSTRACT

A multi-axis waterjet cutting system is disclosed which eliminates high-pressure tubing coils in the area adjacent the waterjet system&#39;s cutting head and isolates critical system components from the backsplash of the cutting process. A high-pressure swivel is combined with an on/off valve arrangement in such a way that these components are closely adjacent the cutting head and rotate therewith, and are substantially shielded from waterjet back-splash. The cutting head and the swivel/valve combination are rotated about the cutting head&#39;s final axis of rotation (e.g., the A-axis) by a drive mechanism substantially shielded by the structure which rotates the cutting head associated with a prior axis of rotation (e.g., the C-axis). 
     By eliminating high pressure tubing coils, the disclosed system reduces the clearance needed for manipulation of the cutting head around the workpiece.

BACKGROUND

The use of high velocity, liquid jets and abrasive-laden liquid jets to precisely cut a variety of materials is well known. Briefly, a high velocity liquid jet is first formed by compressing the liquid (typically water) to an operating pressure of 50,000-90,000 psi or more), and forcing the compressed liquid through an orifice having a diameter approximating that of a human hair; namely, 0.003 to 0.040 inches. The material defining the jet-forming orifice is typically a hard jewel such sapphire, ruby or diamond.

The resulting highly coherent waterjet is discharged from the orifice against a workpiece via a generally tubular cutting nozzle at a velocity which approaches or exceeds the speed of sound. Those skilled in the art will recognize, however, that numerous other liquids can be used without departing from the scope of the invention, and the recitation of the jet as comprising water should not be interpreted as a limitation. Accordingly, the term “waterjet” and “water” as used herein shall include any liquid suitable for cutting a workpiece in the manner described herein.

To enhance the cutting power of the waterjet, abrasive materials have been added to the jet stream to produce an abrasive-laden waterjet, typically called an “abrasivejet”. The abrasivejet is used to effectively cut a wide variety of materials from exceptionally hard materials (such as tool steel, aluminum, cast iron armor plate, certain ceramics and bullet-proof glass) to soft materials (such as lead). Typical abrasive materials include garnet, silica, and aluminum oxide having grit sizes of #36 through #200.

To produce the abrasivejet, the waterjet passes through a “mixing region” wherein a quantity of abrasive is enhanced with kinetic energy from the high speed waterjet, thus enabling abrasive removal of most materials through abrasion. The abrasive material, which is under atmospheric pressure in an external hopper, is drawn into the mixing region by the lower pressure region via a conduit (referred to as the “abrasive feed tube”) that communicates at one end with the interior of the hopper, and at the other end with the mixing region via an abrasive inlet hole formed in the cutting head housing that houses the jet-forming orifice jewel and mixing region.

The resulting abrasive-laden waterjet (or “abrasivejet”) is then discharged against a workpiece through an abrasivejet nozzle that is supported closely adjacent the workpiece. The spent abrasive-laden water is drained away from the workpiece in any of a number of known ways, and collected in a collection tank for recycling of the abrasive and/or proper disposal.

As used hereinafter in this specification and in the claims, and as recognized by those of ordinary skill in the art, the term “waterjet cutting systems” includes abrasivejet cutting systems, the term “waterjet” includes “abrasivejet” within its scope when referring to the jet that is discharged towards the workpiece, and the term “cutting head” refers to a unit comprising a housing that has a high pressure water inlet (and an abrasive inlet if an abrasivejet cutting head), and encloses the orifice member, a mixing region if an abrasivejet cutting head, fluid paths therebetween and required seals in the positions and spatial relationships needed for efficient cutting. The cutting head may also include an on/off actuator that controls the flow of water within the cutting head. As also known to those of ordinary skill the art, The cutting head directs the waterjet/abrasivejet to the workpiece through a discharge nozzle.

To appropriately and precisely position the cutting head with respect to a workpiece, a growing number of waterjet cutting system applications provide translation and/or rotation of the cutting head nozzle (usually referred to as the “cutting tool” or simply the “nozzle”) along and about a plurality of axes to so that the workpiece can be approached from multiple directions.

Those of ordinary skill in the art recognize that the commonly used axes are the “X”, “Y”, “Z”, “A”, “B” and “C” axes. The first three are linear axes; i.e., the cutting head and nozzle are moved linearly in the directions of the X, Y and Z axes. The X and Y axes may correspond, for example, to the length and width of a cutting table underlying the cutting nozzle, while the Z axis corresponds to the height of the cutting nozzle above the cutting table. The A, B, and C axes are axis of rotation; i.e., the cutting head and nozzle rotate about the A, B and C axes. By convention, the C axis is parallel to the Z axis and perpendicular to the X-Y plane. The A axis is perpendicular to the C axis, with its centerline parallel to the X-axis when the C-axis position is zero. The B axis is also perpendicular to the C axis, with its centerline passing through the centerline of the C axis, but orthogonal to the A-axis; in other words, the A axis is parallel to the X-axis, and the B-axis is parallel to the Y-axis when the C-axis position is zero.

This specification will discuss the invention in terms of these standard and commonly used nomenclatures; however, it should be recognized that the invention is not limited by the use of this nomenclature, and that other axes and axis relationships can be used without departing from the scope of the invention.

Existing waterjet cutting systems employ swivels and coils to supply the high pressure cutting liquid to the nozzle. The mechanisms utilized to accommodate the rotational axes of movement have been bulky, and have restricted the positioning of the nozzle vis-à-vis the workpiece, thus limiting the application of waterjet cutting, particularly where multiple axes of rotation are employed. The use of coils that allow movement about these axes is expensive and poses a possible safety hazard due to the common fatigue failure of the coils which, as previously described, are the conduits for up to 50,000 psi or more of pressurized water. In addition, such coils reduce clearance around the cutting head of the system, limiting the orientation of the cutting tool around the workpiece at times.

Swivels are safer but, to limit the size which can add to the bulky size of the mechanism, most manufactures use small ¼-inch high pressure swivels, which have a short mean time between failure as compared to the larger ⅜-inch high-pressure swivels.

SUMMARY

A waterjet cutting system constructed in accordance with the invention herein eliminates high-pressure tubing coils in the area adjacent the waterjet system's cutting head and isolates critical system components from the backsplash of the cutting process. Preferably, a high-pressure swivel is combined with an on/off valve arrangement in such a way that these components are closely adjacent the cutting head but substantially shielded from waterjet back-splash, minimizing the mechanism's size while increasing waterjet back-splash safety and mean time before failure. The cutting head and the swivel/valve combination are rotated about the cutting head's final axis of rotation (described below) by a drive mechanism substantially shielded by structure associated with a prior axis of rotation . . . preferably, the cutting head's prior axis of rotation.

As used in this specification, the term “final axis of rotation” refers to the axis of rotation about which the cutting head is rotated without such rotation moving the position of another rotational axis. As used in this specification, a “prior axis rotation” refers to the axis of rotation about which the cutting head is rotated prior to its rotation about its final axis of rotation. Where the cutting head has both “A” and “B” axes of rotation, the “final axis of rotation” is whichever of the two is moved last.

By eliminating high pressure tubing coils, and thereby reducing the clearance needed to manipulate the cutting head around the workpiece, the preferred system constructed in accordance with the invention also simplifies the kinematics of the multi-axis system, making it easier to be programmed for accurate CNC control while protecting critical components from back-splash to thereby increase mean time to failure.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view in schematic of a cutting head assembly and its preferred rotatable support structure constructed in accordance with the invention for use in a 5-axis waterjet cutting system;

FIG. 2 is a fragmentary top plan view in schematic of the cutting head assembly and support structure of FIG. 1, including a mount bearing that permits it to rotate about the “A” axis;

FIG. 3 is a front elevation view, in schematic, of a preferred cutting head assembly constructed in accordance with the invention, wherein certain internal water paths and bearing assemblies are illustrated in dotted or hidden lines for ease of discussion;

FIGS. 4-6 are each a right side elevation view, in schematic, of a cutting head assembly and an alternative “A”-axis drive assembly constructed in accordance with the invention; and

FIG. 7 is a front elevation view, in schematic, of a cutting head assembly and “z”-axis carriage to which it is mounted, illustrating the preferred internal water-conducting conduit in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a side elevation view in schematic of a cutting head assembly and its preferred rotatable support structure constructed in accordance with the invention for use in a 5-axis waterjet cutting system. FIG. 1 illustrates a preferred example of a shielded swivel/valve combination that rotates with the cutting head about a final axis of rotation, plus a driving mechanism for same shielded within a prior axis' structure. A 5-axis system is described because it is believed to currently be the most widely used of the waterjet cutting systems employing linear and rotational axes, and not by way of limitation. As stated earlier, the term “waterjet” as used herein includes “abrasivejet” within its scope when referring to the cutting system or the jet that is discharged towards the workpiece.

The five exemplary axes employed by the illustrated cutting system are the “X”, “Y”, “Z”, “A” and “C” axes. The illustrated combination in FIG. 1 includes a cutting nozzle 10 that has been rotated about its A-axis into the illustrated 9 o'clock position. Those skilled in the art will recognize that the cutting nozzle 10 moves linearly along the X, Y and Z axes, and rotates about the A and C axes to approach a workpiece from multiple directions. The “X” and “Y” axes may correspond, for example, to the length and width of a cutting table underlying the cutting nozzle, while the Z-axis corresponds to the height of the cutting nozzle above the cutting table.

As illustrated in FIG. 1, the C-axis is perpendicular to the X-Y plane and parallel to the Z-axis, while the A-axis is positioned with its centerline perpendicular to the C-axis. The cutting nozzle 10 is mounted within a cutting head 26 that is, in turn, mounted to a C-axis structure 16. The C-axis structure, in turn, is mounted to a carriage structure (not shown) which can travel along the Z-axis to position the cutting head at the desired height above the cutting table as the cutting process proceeds.

As will be apparent, rotation about the C-axis is not limited by a high pressure water conduit. In FIG. 1, the C-axis structure 16 is schematically illustrated as comprising a generally tubular member 16 which houses an A-axis drive mechanism 14, and also carries a high-pressure water conduit 72 (FIG. 7) that conducts the high pressure water from the swivel 12 at its upstream end to a swivel 18 (FIGS. 1 and 3) at its downstream end that is coupled to the cutting head's high pressure water inlet. The C-axis structure 16 is mounted on the Z-axis carriage (not illustrated) for movement along the Z-axis to position the cutting head 26 at the desired height above the cutting table. The C-axis structure is securely affixed to the Z-axis carriage by a pair of collar-like bearing assemblies 16 a, 16 b which permit the structure 16 to rotate within the collars without movement vis-à-vis the carriage in the Z-axis direction. As will be appreciated, the C-axis structure 16 thereby supports cutting head 26 and rotates it about the C-axis. The swivel 12 at the top of the C-axis structure is axially aligned with the C-axis and preferably has no restrictions on its the total angle of rotation, permitting the C-axis structure 16 and the cutting head 26 to be rotated about the C-axis without restriction. The swivel 12 is preferably far from the waterjet back-splash region, does not interfere with the cutting area

As the C-axis structure rotates, thereby rotating the cutting head, the internal conduit 72 (FIG. 7) rotates about the C-axis as well, its coupling to the cutting head's inlet swivel 18 (FIGS. 1 and 3) rotates with the cutting head and C-axis structure 16 and is thereby maintained without the need for coils. The rotating C-axis structure 16 and its carried high pressure water conduit 72 serve in the elimination of high pressure coils and/or the conventional light weight ¼-inch high-pressure water swivel at the cutting head, and the swivel 18 permits the cutting head to be rotated about the A-axis while remaining coupled to the downstream end of the high pressure line 72.

As illustrated in FIG. 1, the cutting head's A-axis is positioned with its centerline perpendicular to the C-axis. The drive 14 for A-axis rotation, is placed within the C-axis structure 16, and is thereby protected from waterjet splash-back, despite its proximity to the cutting head. This minimizes the size of the cutting head's mechanical components at or near the cutting head. By limiting the size of the mechanical components, the cutting head is able to reach into confines smaller than any other 5-axis waterjet head presently for sale or in use. In practice, it has been found that cutting systems employing the illustrated configuration require a clearance of approximately 9 inches in diameter when the cutting head is rotated compared with the clearance of approximately 18 inches required by known 5-axis systems.

As described below, the preferred A-axis swivel 18 is preferably included within a common housing 23 with a high pressure on/off valve 22. The high pressure valve/swivel combination within the common housing 23 results in the use of larger swivel within less space, permitting use of the relatively larger long-life swivel components without impinging on the positioning constraints that would be imposed by such swivels if used in known 5-axis waterjet cutting systems. This allows for long periods of operation without failure, readily available components and safety without the need of high pressure coils.

Thus, the preferred configuration provides:

-   -   1. the inclusion of both a high pressure water swivel and on/off         valve in a common body;     -   2. a mechanical control system designed such that the critical         components are positioned to be free of the back-splash of the         waterjet cutting process;     -   3. the elimination of any high pressure tubing coils used to         allow rotation of an axis; and     -   4. the positioning of the A-axis perpendicular to the C-axis         thus simplifying the kinematics of the 5 axis system, making it         easier to program.

FIG. 2 is a fragmentary top plan view in schematic of the cutting head assembly and support structure of FIG. 1, including a mount bearing that permits it to rotate about the “A” axis. Those of ordinary skill in the art know that the nozzle 10 is mounted in a cutting head 26 that is typically coupled to a source of high pressure water via an internal passage in an extension tube 28. The extension tube sealingly engages the internal water passage in the on/off valve 22 employing actuator 30 that is pneumatically driven to selectively block or permit the egress of high pressure water into the upstream end of the extension tube. Waterjet and abrasivejet nozzles, cutting heads, extension tubes and on/off actuators, per se, are each well known in the art, and a description of any specific configuration thereof is accordingly omitted for the sake of brevity; this invention is not limited to any specific configuration of same.

FIG. 3 is a front elevation view, in schematic, of a preferred cutting head assembly constructed in accordance with the invention, wherein certain internal water paths and bearing assemblies are illustrated in dotted or hidden lines for ease of discussion. The actuator 30 is illustrated attached to the common housing 23 for visual clarity. Common housing 23, containing the on/off valve 22 and swivel 18, is coupled between on/off actuator 30 and extension tube 28 to permit the passage of hi-pressure water from a water inlet line to the cutting nozzle, the on/off valve 22 and swivel 18 being interconnected via an internal conduit within the common housing. The water inlet line (not shown) is fastened onto the generally tubular shaft 32 of the swivel 18 which is affixed to the common housing. The internal passage of the generally tubular shaft 32 feeds the high pressure water into the on/off valve 22 within the common housing 23. The on/off valve 22 has an inlet passage 35 sealingly coupled to the swivel shaft 32 for that purpose, and an outlet passage 36 sealingly coupled to the inlet passage of the generally tubular extension tube 28.

The on/off valve 22 within the common housing is preferably a needle valve actuated by the on/off actuator 30. The preferred actuator comprises a pneumatically responsive needle (not shown) that selectively blocks fluid communication between the on/off valve's inlet 35 and the valve's outlet 36 in response to a signal from a CNC or other control unit or switch, to activate and deactivate the waterjet/abrasivejet.

The internal passage of the extension tube 28 conducts high pressure water from the on/off valve outlet 36 to the cutting head 26 for discharge as a waterjet or abrasivejet at the downstream end of the cutting nozzle 10. Accordingly, the entire path taken by the high-pressure water exiting from the conduit 72 is internal to the common housing 23, extension tube 28 and cutting head 26 and, therefore, within the portion of the cutting system that rotates about the A-axis (as further described below).

The common housing 23 is preferably supported by the Z-axis carriage structure for movement along the Z-axis in such a way that the actuator 30, extension tube 28 and cutting head 26 are also supported by the carriage structure for movement along the Z-axis. The preferred structure by which this support is provided is schematically illustrated in FIGS. 4-7 as strut arm 38.

In accordance with the preferred embodiment of the invention, the system's A-axis drive 14 is housed within the C-axis structure 16, as illustrated in FIGS. 1 and 4-6. It may be noted that in this embodiment of a 5-axis cutting system, the C-axis is the “prior axis” referred to earlier in this specification, and it may be further noted that the movement of the cutting head about the C-axis only moves the A-axis.

FIGS. 4-6 show examples of A-axis drive mechanisms housed within the C-drive structure, but those of ordinary skill in the art will recognize that the invention is not limited to any particular A-axis drive mechanism, and that other drive mechanisms can be used within the scope of the invention. Turning initially to FIG. 4, the schematically illustrated A-drive mechanism comprises an electric stepping motor 40 which drives a pair of tie rods 44, 46 via a gearbox 42 that is coupled to the proximal ends of the tie rods via a crank arm 43. The tie rods extend generally parallel to the C-axis. The distal ends of the tie rods are coupled to the cutting head 26, preferably via affixation to the exterior of the common housing 23. In operation, the stepping motor is activated under CNC control (or by a control signal from an alternative source) to precisely rotate the cutting head 26 about the A-axis to the desired angular position, acting through the crank arm 43 and tie rods 44, 46.

In accordance with the invention, the A-drive mechanism is substantially enclosed within the C-axis structure and thereby substantially shielded from back-splash from the waterjet cutting process.

The alternative drive mechanism schematically illustrated in FIG. 5 comprises a helically-threaded shaft 50 which is controllably rotated by the stepping motor 40, and a coupling block 52 which engages the threaded shaft to move linearly in a path generally parallel to the C-axis and thereby cause rotation of the cutting head about the A-axis via a set of linkages 54, 56 coupled to the exterior of the common housing 23.

In FIG. 6, a belt and pulley system is utilized to rotate the cutting head about the A-axis. A split belt 60 is coupled at one end to a first coupling block 62, and extends upward therefrom, around an idler pulley 66 and then downward towards and around a driven pulley 67 to a second coupling block 64, to which the belt's other end is affixed. The coupling blocks, in turn, are mounted on (or integral with) a carriage 68 that engages a threaded shaft controllably rotated by a stepping motor 40 to move the carriage 68 linearly in a path generally parallel to the C-axis and thereby cause rotation of the cutting head about the A-axis via belt 60 and the driven pulley 67, which is coupled to the exterior of the common housing 23 and whose axis of rotation is preferably co-axially aligned with the A-axis. The driven pulley 67 is mounted at 76 (FIG. 3) about an arm 78 of the common body 23 for that purpose.

As described earlier, the common housing 23 is preferably supported by the Z-axis carriage structure for movement along the Z-axis in such a way that the actuator 30, extension tube 28 and cutting head 26 are also supported by the carriage structure for movement along the Z-axis. More precisely, and as further described above, the common housing, actuator, extension tube and cutting head affixed to the C-axis structure which, in turn, is supported by the Z-axis carriage. The common housing 23 is preferably supported by the strut arm 38 of the C-axis structure 16 (FIGS. 4, 5) via a high angular contact bearing unit 24 a (FIG. 3) coupled to the arm 78 of the common body. The bearing unit 24 a allows rotation of the cutting head about the A-axis, and prevents longitudinal motion along the A-axis. Those of ordinary skill in the art will recognize that the common housing can alternatively be an integral part of the cutting head, with the resulting cutting head housing being configured to shield the swivel 18 and on/off valve 22 from waterjet backsplash.

While the foregoing embodiment is, for the reasons stated above, a 5-axis configuration, those skilled in the art will recognize that the invention herein is not so limited and may be applied to any number of axis having any number of orientations and relationships. Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention, which is defined by the appended claims. 

I claim:
 1. A waterjet cutting system comprising: a cutting head; structure for selectively and controllably translating and rotating the cutting head with respect to a plurality of axes so as to permit the cutting head to approach a workpiece from a desired direction, there being at least two axes of rotation of which rotation about one axis of rotation does not change the position of the other axis of rotation; a high-pressure water-conducting swivel in serial fluidic communication with an on/off valve, and positioned with said valve in such a way that the swivel and valve are closely adjacent the cutting head for translation and rotation therewith, the swivel and valve being substantially shielded from waterjet back-splash; structure supporting the cutting head and rotating with said cutting head about said other axis of rotation; and a drive mechanism for rotating the cutting head about said one axis of rotation, said drive mechanism being substantially housed within said supporting and rotating structure.
 2. The cutting system of claim 1 wherein said one axis of rotation is the A-axis, and said other axis of rotation is the C-axis associated with the waterjet cutting system.
 3. A waterjet cutting system comprising: a cutting head for producing a waterjet and directing the waterjet at a workpiece; a C-axis structure for supporting and rotating the cutting head about the C-axis; a hi-pressure water-conducting swivel and a valve serially coupled in fluidic communication to conduct high pressure water from an exterior source to the cutting head, said swivel and valve being mounted adjacent to the cutting head for rotation therewith about at least one axis of rotation other than the C-axis; a shielding structure mounted for rotation with the cutting head and positioned to shield the swivel and valve from waterjet back-splash ; and a drive mechanism for controllably rotating the cutting head about said other axis of rotation, said drive mechanism being supported substantially within the C-axis structure in such a way as to refrain from interfering with the clearance between the cutting head and workpiece while being substantially shielded from waterjet back-splash, said C-axis structure including an internal fluid path for conducting high pressure water from an external source to said serially coupled water-conducting swivel and valve.
 4. The cutting system of claim 3 wherein the internal fluid path of the C-axis structure has upstream and downstream ends, and further including a second swivel in fluid communication with the upstream end of the internal fluid path to couple the internal fluid path to the external high pressure water source while permitting the C-axis structure to rotate about the C-axis.
 5. The waterjet cutting system of claim 3 wherein the shielding structure forms a portion of the cutting head housing.
 6. The waterjet cutting system of claim 3 wherein the shielding structure is a housing coupled to the cutting head for rotation therewith and substantially enclosing the swivel and on/off valve.
 7. The cutting system of claim 3 wherein said one axis of rotation is selected from the A-axis and the B-axis.
 8. The cutting system of claim 3 including an actuator 30 operative on the valve responsive to a control signal to selectively block and permit fluid flow through the valve to deactivate and activate production of the waterjet.
 9. A waterjet cutting system comprising: cutting head having a housing that has a high pressure water inlet, a jet-forming orifice-defining member, an internal fluid path for conducting high pressure water from the inlet to the orifice-defining member and a discharge fluid path for discharging the waterjet from the cutting head, said cutting head being configured to accept a cutting nozzle within its discharge path to direct the discharged jet against a workpiece; a cutting head inlet swivel mounted to the cutting head at its water inlet to conduct high-pressure water into the cutting head's internal fluid path; a carriage for controllably adjusting the height of the cutting head in response to a control signal when the cutting head is mounted to the carriage, said adjustment being along a Z-axis of translation; a C-axis member mounted on the carriage for supporting the cutting head, the C-axis member being rotatable about a C-axis of rotation that is parallel to the Z axis, the cutting head being supported by the C-axis member for rotation therewith, the C-axis member having an upstream fluid inlet, a relatively downstream fluid outlet, and an internal passageway therebetween for permitting the flow of high-pressure water from the inlet and through the outlet via the internal passageway, a C-axis swivel within the upstream fluid inlet of the C-axis structure for conducting high-pressure water from an external source to the C-axis member's internal passageway a swivel/valve combination including a high-pressure water-conducting swivel in serially disposed fluidic communication with an on/off valve mounted on the C-axis structure and mechanically coupling the cutting head to the C-axis structure, the swivel/valve combination being mounted to the C-axis structure for rotation about an axis that is perpendicular to the C-axis, whereby the swivel/valve combination and cutting head can rotate about the C-axis and said perpendicular axis in response to respective control signals, a conduit for conducting the high-pressure water passing through the C-axis member into the swivel of the swivel/valve combination, the valve of said combination having an outlet fluidically coupled to the inlet of said cutting head and configured to selectively block the flow of high pressure water from the C-axis structure from entering the cutting head; a drive mechanism for rotating the swivel/valve combination and the coupled cutting head about said perpendicular axis, said C-axis structure having an internal cavity for substantially housing the drive mechanism.
 10. The cutting system of claim 9 wherein the internal cavity of the C-axis member is adjacent the valve/swivel combination.
 11. The cutting system of claim 9 including a protective housing substantially enclosing the valve/swivel combination.
 12. The cutting system of claim 11 wherein the protective housing is spaced from the cutting head.
 13. The cutting system of claim 9 wherein the valve of the swivel/valve combination is a needle valve.
 14. The cutting system of claim 9 wherein the C-axis swivel is axially aligned with the C-axis.
 15. The cutting system of claim 9 wherein the drive mechanism includes an electric stepping motor, a pair of tie rods driven by the motor and coupled the cutting head to rotate the cutting head about said perpendicular axis to a desired angular position.
 16. The cutting system of claim 9 wherein the drive mechanism includes an electric stepping motor, a helically-threaded shaft controllably rotated by the stepping motor, and a coupling block that engages the threaded shaft to move linearly in a path generally parallel to the C-axis, and a set of linkages coupled to the coupling block and to the cutting head to cause rotation of the cutting head about said perpendicular axis in response to said linear movement of the coupling block.
 17. The cutting system of claim 9 wherein the drive mechanism includes an electric stepping motor and a belt and pulley system for rotating the cutting head about said perpendicular axis, the belt and pulley system including a split belt, an idler pulley, a driven pulley first and second coupling blocks, a carriage and a threaded shaft, the driven pulley having an axis of rotation generally aligned with said perpendicular axis and coupled to the cutting head to rotate the coupling head about said perpendicular axis when rotated, the split belt being coupled at one end to the first coupling block and extending therefrom around the idler pulley, and then towards and around the driven pulley to the second coupling block, to which the belt's other end is affixed, said coupling block being mounted on or integral with the carriage, the carriage engaging the threaded shaft, the threaded shaft being controllably rotated by the stepping motor to move the carriage generally linearly in a path generally parallel to the C-axis to thereby cause rotation of the driven pulley and cutting head about said perpendicular axis via the belt.
 18. The cutting system of claim 17 including a protective housing spaced from the cutting head and substantially enclosing the valve/swivel combination, said protective housing having a support arm extending generally parallel to said perpendicular axis, the driven pulley being mounted generally about said arm of the protective housing to rotate the housing and cutting head about said perpendicular axis. 